1. Field of the Invention
This invention relates to an optical disc device which utilizes a light beam from a laser or other light source to optically record information onto an information carrier or reproduce information from an information carrier, and to a track jumping control circuit and focus jumping control circuit used in this device; more specifically, this invention relates to track jumping control for movement from a track to another adjacent track, and to focus jumping control for movement from one data surface to another adjacent data surface in an information carrier having a plurality of data surfaces.
2. Description of the Related Art
When seeking a desired track in an optical disc device of the prior art, if the movement distance to the track is long, the entire optical head comprising the tracking actuator is moved in the radial direction of the information carrier with tracking operation halted, and by counting the number of tracks traversed on the information carrier by the light beam, the light beam is moved to the desired track.
On the other hand, when the number of tracks to the desired track is several tracks, acceleration/deceleration pulses are applied to the tracking actuator while performing tracking operation in order to reliably and stably reach the desired track, and by repeating track jumping to adjacent tracks the light beam is moved to the desired track on the information carrier. As the most basic method of such track jumping control, an acceleration pulse with a prescribed peak value is output for a prescribed length of time, and when a TE (tracking error) signal zero-cross point is subsequently detected, a deceleration pulse with a prescribed peak value is output for a prescribed length of time.
In an information carrier having a plurality of data surfaces, focus jumping control to move from one data surface to another adjacent data surface generally is performed similarly to track jumping control, by applying acceleration/deceleration pulses with prescribed peak values and for prescribed lengths of time to the focus actuator.
In the above track jumping control, as another track jumping method, Japanese Patent Laid-open No. 5-234103 discloses a method in which an acceleration pulse with prescribed peak value is output until the TE signal zero-cross point, after which a deceleration pulse with the same peak value as the acceleration pulse is output until a certain level of the TE signal prior to the on-track state is detected. And, Japanese Patent Laid-open No. 2000-353324 discloses a method in which an acceleration pulse with a prescribed peak value is output until a certain level of the TE signal is detected, and the peak value of the deceleration pulse output after detection of the TE signal zero-cross point is varied according to the time from the initiation of acceleration until this level is detected.
However, in the former track jumping method an acceleration or deceleration pulse with the same peak value is applied, until the TE signal zero-cross point in the case of acceleration, and until before the TE signal on-track state in the case of deceleration, so that the energy applied to the tracking actuator is different during acceleration and during deceleration. Consequently the velocity of motion of the light beam after the end of the deceleration pulse cannot be reduced sufficiently, and track jumping becomes unstable. Also, when the device is subjected to vibrations, there is partial eccentricity of optical discs, or other external disturbances occur, there is scattering in the velocity of motion of the light beam after the end of the deceleration pulse, and track jumping becomes unstable.
On the other hand, in the latter track jumping method stable track jumping is possible even when there are external disturbances, but detection of external disturbances is based on the time of motion from the initiation of acceleration to a certain location. Hence even when there are no external disturbances, scattering may occur in the time of motion from the initiation of acceleration to a certain location due to TE signal amplitude fluctuations arising from scattering in the optical disc track pitch, and it is difficult to separate external disturbances from scattering in the track pitch, so that track jumping may become unstable.